1. Field of the Invention
The present invention relates to a polishing liquid which is used in manufacturing processes for semiconductor devices and a polishing method using the polishing liquid. Specifically, the invention relates to a polishing liquid and a polishing method, which are used for chemical mechanical polishing for planarization in a wiring process for a semiconductor device.
2. Description of the Related Art
In the development of semiconductor devices typically represented by semiconductor integrated circuits such as large scale integrated circuits (hereinafter sometimes referred to as “LSI”), increased density and integration through refining and lamination of wirings has been demanded in recent years in order to decrease the size and increase the operation speed of semiconductor devices. For this purpose, various techniques such as chemical mechanical polishing (hereinafter sometimes referred to as “CMP”) have been used. CMP is a technique essential for carrying out surface planarization of a processed film such as an inter-layer insulating film, formation of plugs, formation of buried metal wirings, etc., and this technique is effective for smoothing a substrate, removing excess of a metal thin film, or removing excess of a barrier layer on the insulating film upon wiring formation.
CMP generally involves bonding a polishing pad on a circular polishing platen (platen), dipping the surface of the polishing pad in a polishing liquid, pressing the surface of a substrate (wafer) to the pad, rotating both the polishing platen and the substrate while a predetermined pressure (polishing pressure) is applied from the rear face thereof to planarize the surface of the substrate by generated mechanical friction.
When manufacturing a semiconductor device such as an LSI, fine wirings are formed in a multi-layer component. When forming metal wirings formed from Cu or the like in each of the layers, a barrier metal film formed from Ta, TaN, Ti, TiN, or the like is formed before the formation of metal wirings in view of preventing diffusion of the wiring material to the inter-layer insulating film or improving the adhesion of the wiring material.
In general, in order to form each of the wiring layers, one or more metal layers are subjected to CMP to remove excess wiring material applied by a plating method or the like (hereinafter sometimes referred to as “metal film CMP”), and then a barrier metal material (barrier metal), the surface of which has been exposed by the metal film CMP, is subjected to CMP (hereinafter sometimes referred to as “barrier metal CMP”).
The polishing liquid used in CMP generally includes abrasive grains (for example, alumina or silica) and an oxidizing agent (for example, hydrogen peroxide or persulfate). The basic mechanism of CMP is considered to be as follows: the metal surface is first oxidized by an oxidizing agent and the resultant oxide film is removed and polished by abrasive grains.
However, CMP using a polishing liquid including such solid abrasive grains sometimes results in scratching, excessive polishing of the entire surface to be polished (thinning), a phenomenon in which a portion of the polished metal surface is excessively polished whereby a dish-shaped recess is formed on the surface (dishing), a phenomenon in which an insulator placed between metal wirings is excessively polished and only the central portions of plural wiring metal surfaces are deeply polished whereby dish-shaped recesses are formed on the surfaces (erosion), and the like.
The use of a polishing liquid including solid abrasive grains usually involves a complicated cleaning step to remove the polishing liquid remaining on the surface of a semiconductor after polishing. Further, treatment of the liquid (liquid waste) after cleaning is costly due to the need to separate out solid abrasive grains by sedimentation.
Further, since the most of the polishing liquid consists of water, there arise problems, for example, in transportation and storage of a vessel that houses the polishing liquid, and savings in production costs have been demanded.
Various ideas have been proposed for a polishing liquid including solid abrasive grains as described below.
For example, a concentrated polishing liquid and a polishing method using the polishing liquid, which are capable of suppressing erosion and scratching have been proposed (for example, refer to Japanese Patent Application Laid-Open (JP-A) Nos. 2000-252242 and 2004-146840).
However, while the above concentrated polishing liquids address the above problem of transportation or storage of containers, a polishing liquid capable of sufficiently inhibiting scratching caused by aggregation of solid abrasive grains and having good storage stability has not yet been obtained at present.